Proton electrolyte membranes (PEMs) may be utilized in various devices including fuel cells, purification and reforming cells as well as in other electrochemical applications.
Various materials have been investigated for use as PEMs. Examples include perfluorosulfonic polymers, as well as various imidazole polymers including polybenzimidazole-H3PO4, polyvinazine HPO4, as well as other imidazole based materials. Imidazole is an aromatic heterocycle having two nitrogen atoms on a ring. Imidazole conducts protons through intermolecular proton transfer or structure diffusion. However, the electrochemical stability of imidazole ring based materials appears to be inadequate for fuel cell applications.
Metals contained within PEM fuel cells such as platinum or other catalysts have the ability to form strong bonds with nitrogen contained within the imidazole rings such that the catalyst will become poisoned or less active. Additionally, oxidation of imidazole in the potential region of oxygen reduction as well as the oxidation of products of imidazole may be absorbed onto the surface of a precious metal catalyst or electrode thereby reducing the efficacy of the electrode surface area.
There is therefore a need in the art for a proton conducting polymer for use in fuel cells that has a high proton conductivity but is not subject to varying efficacy at various humidity values and at temperatures above 100° C. Additionally, there is a need in the art for a proton conducting polymer that has a chemical stability and compatibility with a precious metal catalyst in a fuel cell environment.